Californian Sea Lion
Being sexually dimorphic, they differ in size, shape, and colouration between the sexes. Males are typically around 2.4 m long and weigh up to 350 kg, while females are typically around 1.8 m and weigh up to 100 kg. Females and juveniles have a tawny brown pelage, although they may be temporarily light grey or silver after moulting. The pelage of adult males can be anywhere from light brown to black but is typically dark brown.
The face of adult males may also be light tan in some areas. Pups have a black or dark brown pelage at birth. Although the species has a slender build, adult males have robust necks, chests, and shoulders. Adult males also have a protruding crest which gives them a high, domed forehead; it is tufted with white hairs. They also have manes, which are less developed than those of adult male South American and Steller sea lions. Both sexes have long, narrow muzzles.
Habitat
Californian sea lions are found on the west coast of North America from Oregon, south to Mexico. Their rookeries (or breeding grounds) are found on offshore islands. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of California. They are generally found in waters over the continental shelf and slope zones; they also frequent coastal areas, including bays, harbours and river mouths.
Diet
California sea lions feed on a wide variety of seafood, mainly squid and fish, and sometimes clams. Commonly eaten fish and squid species include salmon, hake, Pacific whiting, anchovy, herring, rockfish, lamprey, dogfish, and market squid. They mostly forage near mainland coastlines, the continental shelf, and seamounts. They may also search along the ocean bottom. California sea lions may eat alone or in small to large groups, depending on the amount of food available. They sometimes cooperate with other predators, such as dolphins, porpoises, and seabirds, when hunting large schools of fish. Sea lions sometimes follow dolphins and exploit their hunting efforts. Adult females feed between 10–100 km from shore. Males may forage as far as 450 km from shore when water temperatures rise. They also have learned to feed on steelhead and salmon below fish ladders at Bonneville Dam and at other locations where fish must queue in order to pass through dams and locks that block their passage.
Breeding
They breed gregariously between May and August when they arrive at their breeding rookeries. When establishing a territory, the males will try to increase their chances of reproducing by staying on the rookery for as long as possible. During this time, they will fast, relying on a thick layer of fat called blubber for energy. Size and patience allow a male to defend his territory more effectively; the bigger the male, the more blubber he can store and the longer he can wait. A male sea lion usually keeps his territory for around 27 days. Females have long parturition intervals, and thus the males do not establish their territories until after the females give birth. Most fights occur during this time. After this, the males rely on ritualized displays (vocalizations, head-shaking, stares, bluff lunges, and so on) to maintain their territorial boundaries. Since temperatures can reach over 30 °C during this time, males must include water within their territories. Some territories are underwater, particularly those near steep cliffs. Sea lions that fail to establish a territory are driven out to sea or gather at a nearby beach.
Before mating begins, females gather into milling groups of 2–20 individuals. The females in these groups will mount each other as well as the males. These groups begin to disintegrate as the females begin to mate. The territorial and mating system of the California sea lion has been described as similar to a lek system, as females appear to choose their mates while moving through different territories. They avoid males that are too aggressive or energetic. Males are usually unable to prevent females from leaving their territories, particularly in water. Mating may occur outside the rookeries, between non-territorial males and females, as the latter move to and from the mating site. In some rookeries, copulation may be monopolized by a few males, while at others, a single male may sire no more than four pups. Female California sea lions have a 12-month reproductive cycle, consisting of a 9-month actual gestation and 3-month delayed implantation of the fertilized egg before giving birth in June or July. Interbirth intervals are particularly long for this species, being 21 days for sea lions off California and more than 30 days for sea lions in the Gulf of California. Females remain with their pups onshore for 10 days and nurse them. After this, females will go on foraging trips lasting as long as three days, returning to nurse their pups for up to a day. Pups left onshore tend to gather in nurseries to socialize and play. When returning from a trip, females call their pups with distinctive calls to which the pups will reply in kind. A mother and pup can distinguish each other's calls from those of other mothers and pups. At first, reunions largely depend on the efforts of the mothers. However, as pups get older, they get more involved in reunions. Older pups may sometimes join their mothers during their foraging trips. Adult male California sea lions play no role in raising pups, but they do take more interest in them than adult males of other otariid species; they have even been observed to help shield swimming pups from predators. Pups are weaned by a year but can continue to suckle for another year.
Population
It is not possible to directly count individuals in order to obtain the total population size because not all age- and sex-classes are onshore at the same time. Therefore, the size of the population is estimated based on the number of births and the proportion of pups in the population following the methods developed. Pups are the only age class constantly on land during the reproductive season, and thus they are used as a reference point in estimating the other age classes. The 2007 minimum population on the Channel Islands and at haul-out sites located between Point Conception and Point Reyes was 153,337. For the same year, the estimated total population in the USA was estimated at 296,750. In Mexico, the species occupies both sides of the Baja California Peninsula. In 2010, the total population size on the Pacific coast was 58,859 individuals while the population in the Gulf of California consisted of 32,037 individuals (Aurioles-Gamboa, unpublished data). Thus, the total population of California Sea Lions is approximately 387,646. They are classed as Least Concern(LC) on the IUCN Red List and there population trend is increasing.
Threats
Conflicts with fisheries, poaching and entanglement in marine debris contribute to California Sea Lion mortality. Prey availability is greatly reduced during El Niño events and large numbers of pups born during these periods die of starvation, as do weaker animals of all age classes. Sea lion rookeries in the Gulf of California do not appear to be greatly influenced by El Niño events. California Sea Lions accumulate pollutants through the food chain, and large amounts of DDT and PCBs discharged in the past continue to accumulate in coastal marine food chains that include this species. California Sea Lions occasionally die of paralytic shellfish poisoning caused by domoic acid, a biotoxin produced by diatom blooms that enter the food web through planktivorous fish, such as Herring and Sardines. Diseases also contribute to California Sea Lion mortality, including some contracted from terrestrial animals, like leptospirosis, an endemic disease with periodic epidemics of acute disease. Contact with feral and domestic dogs and other terrestrial animals may expose the species to additional diseases like brucellosis, which may cause miscarriages.
Conservation
Protection, which began in the mid-20th century in the United States, was solidified with the passage of the U.S. Marine Mammal Protection Act of 1972 and similar laws in Mexico. These protective measures provided the impetus for recovery of the population. At coastal sites and on most offshore islands, tourism is highly regulated and controlled. The National Marine Fisheries Service regularly monitors the California Sea Lion population in US waters. The Mexican federal government’s Comisión Nacional de Areas Naturales Protegidas (National Commission of Natural Protected Areas) has conducted annual censuses and monitored the health of the California Sea Lion populations in the Gulf of California since 2011.